It is well known that reverse flotation performance of iron oxides is affected by water quality. Since many potential variations among water sources recycling in a mineral processing plant bring unpredictable effects on the flotation system of iron oxides: disturbing ions/compounds, pH, hardness, residual reagents, etc. In this study, the recycled tailing water from a local plant, characteristically constituting of Ca²⁺, Mg²⁺, Na⁺, K⁺, Al³⁺, Fe³⁺, Cl⁻, SO₄²⁻ etc., was introduced into the cationic reverse flotation process of an iron ore. A series of bench flotation tests using iron ores, micro-flotation tests using pure fine quartz, water chemical analyses, and zeta potential measurement were conducted with the objective of identifying the possible influences of both cations and anions in the recycled tailing water on the flotation performance. The flotation results pointed out that the cation with higher valency had more severe influences on the recovery of iron oxides. The formation of the pH-dependent surface complexes on mineral surfaces, for example, Fe(OH)⁺, Fe(OH)²⁺, and Fe(OH)₃ resulted from Fe³⁺ ions adsorption, contributed to the less negative zeta potentials of the quartz, and consequently weakened its interaction with the amine collector. It is worthy to note that SO₄²⁻ ions seem to have a more positive effect on the recovery of iron oxides than Cl⁻ ions. This is probably attributed to the formation of inner/outer- sphere surface complexes on the iron oxides, inhibiting the dissolution of the iron ions/species, and the coordination with these cations from the recycled tailing water, shielding their disturbances in the flotation.

Selective flocculation of heating or caustic-digested starch on hematite is well practical. What happens to the starch from alkali-digestion at room temperature or heating-treatment, however, may not be fully understood. An attempt to identifying possible effects of heating- or caustic-digested starch on its adsorption characteristics on fine hematite was made through a series of tests, like adsorption test, micro-flotation test, turbidities test, Fourier transform infrared spectroscopic analysis (FTIR), and Aggregation/dispersion measurement as well. All results from these tests pointed out that those traditional digestion methods have a significant influence on adsorption density of starch on mineral surfaces, as well as its adsorption mechanisms. Since a certain amount of carboxyl groups on the starch remnants resulted from heating- or caustic-digestion probably attributes to the acid/base interaction between the starch and hematite. And much more amounts of carboxyl groups seem to be harvested from the starch digested with sodium/potassium hydroxide at higher concentrations. But the homogeneous and transparent starch gel from alkali-digestion at a concentration of more than 2% at room temperature, consisting of a great many short-chain remnants, may probably weaken its flocculating capacity on hematite and lead to performing a potentially dispersing role instead. It is also worthy to notice that the starch gel from a combination of caustic-digestion at a 1.5 weight ratio of sodium hydroxide to starch and heating-treatment at the temperature of 100°C reached an adsorption density of almost 12 mg/g hematite, compared with 9.0 mg/g from caustic-digested starch at same concentration or 6.2 mg/g from heating-treated starch in boiling water only.

The flotation separation of magnetite and quartz is a long-term challenge for the beneficiation industry. For high-quartz magnetite, conventional flotation shows poor separation effect, resulting in the waste of resources and low flotation efficiency. In this paper, dodecylamine acts as a collector and Al(III) ions in water act as a depressant to selectively separate magnetite and quartz at high alkalinity. The experimental results are analyzed by a micro-flotation experiment, solution chemical calculation, zeta potential, contact angle measurement, and Fourier transform infrared spectroscopy (FTIR). The results of micro-flotation experiments showed that Al(III) ions in water inhibited magnetite more strongly than quartz. The calculation results of solution stoichiometry and zeta potential showed that the phase formed by Al(III) ions on the surface of magnetite and quartz are mainly Al(OH)_3(s), which covers the surface of magnetite and quartz, The contact angle measurement results showed that with the addition of Al(III) ions, the contact angle of magnetite varies significantly than that of quartz, and the floatability of magnetite is lower than that of quartz. The FT-IR results further indicated that the addition of Al(III) ions could hinder the adsorption of dodecylamine on the magnetite surface. Meanwhile, the addition of Al(III) ions has no obvious effect on the adsorption of dodecylamine on the quartz surface.

An investigation on these adsorption characteristics of heating-treated starch on fine hematite was conducted through a series of tests, like adsorption tests, zeta potential tests, micro-flotation tests and Fourier transform infrared spectroscopic analysis as well. All results pointed out that different temperature of starch heating treatment tends to achieve different degree of starch gelatinization, probably contributing to its different flocculating capacities on mineral surfaces. Since such differences on the degree of starch gelatinization after heating-treatment seem to induce distinct amounts of adsorption densities and flocculated recoveries on hematite. And the higher the water temperature is, the better the starch gel would be.

Water quality, particularly hardness, plays an important role in affecting the floatability of minerals as it interferes with the chemical/electro-chemical characteristics of mineral surfaces and their interactions with flotation reagents. It could become unpredictable when water sources characterized by different calcium or magnesium ion distributions were involved. This study aimed to identify the role of Ca2+/Mg2+ ions in the recycled water on the cationic reverse flotation selectivity of iron oxides through a series of bench/micro flotation tests, zeta potential, powder contact angle, and Fourier Transform Infrared (FTIR), etc. The results pointed out that the use of recycled tailing water deteriorates the flotation selectivity and dilutes the concentrates. This can be largely attributed to the presence of Ca2+ ions at higher concentrations as they induce a drop in the Fe recovery and an increase in SiO2 content while an increase in the content of Mg2+ ions seems to have little effect on the quality of concentrate. As evidenced by the data from micro-flotation, powder contact angle, zeta potentials, and FTIR, a hydrophilic colloidal layer formed by Ca-based hydrolyzed compounds, such as Ca(OH)+ or, CaCO3(s), etc., on quartz could change its zeta potentials and disturb its interactions with a cationic collector. They also play a role in weakening the flocculation of starch on hematite probably by pre-locking the acidic groups on the starch remnants and contracting their configurations, thus preventing their adsorption on mineral surfaces. However, magnesium ions seem to be beneficial to in strengthening the flocculation of starch on hematite as magnesium-based species could act as adsorption bridges of between starch and mineral surfaces.

It is inevitable for the occurrences of pulp pH buffering during pH control in flotation as the minerals with acidic/alkali properties tend to interact with pH modifiers and restore the pulp pH. This could result in some disturbing ions and alter the water/pulp chemistry. The purpose of this...